1. Field of the Invention
This invention relates generally to microwave coaxial connectors; and more particularly to connectors that can be mass produced very economically but that have extremely (and reliably) low reflections and losses.
2. Developments in This Field
It has been realized for some decades that in coaxial-connector performance a major limiting factor, comparable in importance to direct reflection and dielectric loss, is connector susceptibility to transverse cavity-mode resonances. Resonances too reflect and absorb power, thereby increasing voltage standing-wave ratio (VSWR) values and degrading transmission.
For example, the coaxial-connector cavity-resonator problem is discussed in U.S. Pat. No. 3,340,495, issued Sept. 5, 1967, and entitled "Ultra-High Frequency Connector"--of which one of the present inventors was a patentee (as coinventor with Weinschel and Elste). In qualitative terms, the general presentation of the cavity-resonance problem in that patent remains valid today.
At that time, however, 18 GHz was considered an ultrahigh frequency, and reflections of perhaps 30 dB below the signal level were regarded as negligible. Since then, frequency demands have increased steadily in a bandwidth-starved technology. Meanwhile demands for precision in microwave instrumentation, and especially in microwave metrology, have escalated continuously.
As a result, state-of-the-art frequency requirements now extend from 26 GHz to well above 60 GHz. Furthermore, in some situations, discontinuities as much as 55 to 60 dB below the signal level are considered significant.
Consequently, minuscule variations in component dimensions during connector mating have become major problems. Thus the connector manufacturer is squeezed for inhumanly tiny tolerances, but also at the same time for price--which is to say, for the utmost in economy, reliability, and yield in the manufacturing process.
A coaxial connector must perform two functions' it must provide contact between the central conductors (and between the outer conductors) of two mating devices; and it must provide support for each central conductor within its outer conductor. In analyzing the limiting factors of coaxial-connector configurations, it is helpful to consider separately the contact function and the support function.